Pentafluoroethane or HFC-125 is a stratospherically safe substitute for dichlorodifluoromethane (CFC-12) and chloropentafluoroethane (CFC-115) in refrigerant and sterilant gas applications. Methods for the production of HFC-125 are well known in the art. See, for example, U.S. Pat. No. 3,755,477. The problem with these processes is that they produce large amounts of CFC-115 as a by-product which must be removed in order to comply with the Program for Alternative Fluorocarbon Toxicity Testing (PAFT) guidelines for product purity. PAFT requires that no more than 0.5% CFC-115 can be present in HFC-125. In addition, still lower levels of CFC-115 (i.e., &lt;0.5%) are desirable to eliminate any ozone depletion risk.
Because CFC-115 forms an azeotrope with HFC-125, see U.S. Pat. No. 3,505,233, it is hard to remove using conventional separation techniques such as simple distillation. The art has therefore looked to extractive distillation techniques to separate these materials. See U.S. Pat. No. 5,087,329 which utilizes a 1-4 carbon fluorocarbon which optionally contains hydrogen and/or chlorine and has a boiling point of -39.degree. C&lt;e.a.&lt;50.degree. C. to increase the relative volatility of HFC-125 so that it can be more easily removed from the mixture. The problem with extractive distillation is that it adds cost and time, requiring yet another distillation step to recover the extracting agent.
Applicants have discovered a process for the removal of CFC-115 from HFC-125 which overcomes these drawbacks and results in the production of high purity HFC-125 in high yield.